The present invention relates to a valve operating mechanism for an internal combustion engine, including a camshaft rotatable in synchronism with the rotation of the internal combustion engine and having integral cams for operating an intake or exhaust valve, and rocker arms or cam followers angularly movably supported on a rocker shaft for opening and closing the intake or exhaust valve in response to rotation of the cams.
Valve operating mechanisms used in internal combustion engines are generally designed to meet requirements for high-speed operation of the engines. The valve diameter and valve lift are selected to efficiently introduce an air-fuel mixture required to produce maximum engine power in a certain engine speed range.
If an intake valve is actuated at constant valve timing and valve lift throughout a full engine speed range from low to high speeds, then the speed of flow of an air-fuel mixture into the combustion chamber varies from engine speed to engine speed since the amount of air-fuel mixture varies from engine speed to engine speed. At low engine speeds, the speed of flow of the air-fuel mixture is lowered and the air-full mixture is subject to less turbulence in the combustion chamber, resulting in slow combustion therein. Therefore, the combustion efficiency is reduced and so is the fuel economy, and the knocking prevention margin is lowered due to the slow combustion.
One solution to the above problems is disclosed in Japanese Laid-Open Patent Publication No. 59(1984)-226216. According to the disclosed arrangement, some of the intake or exhaust valves remain closed when the engine operates at a low speed, whereas all of the intake or exhaust valves are operated, i.e., alternately opened and closed, during high-speed operation of the engine. Therefore, the valves are controlled differently in low-and high-speed ranges. However, if the valve control were effected in different modes in more speed ranges, the engine output power would be increased and the fuel economy would be improved. Furthermore, if the intake or exhaust valve of a particular engine cylinder of a multicylinder internal combustion engine could be kept inoperative in order to make the particular engine cylinder substantially inactive, fuel consumption would be reduced by stopping the operation of the intake or exhaust valve of the particular engine cylinder while the engine operates in a low-speed range. However, no satisfactory devices have been available in the past to achieve such a task.